The present invention relates generally to an optical detector for use in a camera or like instrument and, more particularly, to an optical detector having reduced sensitivity to stray light and to a method of producing an optical detector with reduced sensitivity to stray light.
As illustrated in FIG. 5, a known optical detector for use in a camera or the like has an IC b used for performing range-finding functions. The IC b is located rearward of a cylinder a used for blocking extraneous light. A lens member c is placed forward of the cylinder a with respect to incident light, and the lens member focuses incident light and projects the focused light through the cylinder a, whereupon it is incident on a light detecting element in the IC b so that processing can be performed to determine information such as distance, light level, and the like.
In the known optical detector, the lens member c typically comprises a transparent plastic member integrally molded in the form of a single piece of plastic material. For proper positioning of the lens member c relative to the cylinder a, a pair of protrusions (referred to herein at times as assembly protruding portions) d extend from both longitudinal end surfaces of the lens member c. The lens member c is assembled over the cylinder a, which has recesses or recessed portions (referred to at times herein as assembly recessed portions) e formed therein in correspondence with the assembly protruding portions d. As shown, the protruding portions d and recessed portions e are formed so as to engage each other such as by a friction or snap fit. Alternatively, the recesses e may simply be formed to properly orient the lens member c in proper position with respect to the cylinder a.
Since the lens member c is formed of injection molded plastic, an additional protrusion (referred to herein interchangeably as a gate trace portion, an injection molding port trace portion, or simply a trace portion) f, formed at a location on the lens member c facing an injection port where plastic material is supplied to a mold cavity during molding of the lens member, extends from the lower end surface of the lens member c. In other words, because the lens member c is an injection molded part, a trace portion of plastic material forms an additional projection at a location of an injection port of an injection molding machine used to fabricate the lens member c. To accommodate the trace portion f so that the lens member c is properly received by the cylinder a, an additional recess a must be formed in the cylinder a.
Another optical detector is shown in FIG. 6. As illustrated, a pair of protrusions i used for assembly extend from vertically opposite end surfaces of a lens member h. A corresponding pair of recesses or recessed portions k are formed in the top and bottom surfaces of a cylinder j. The protrusions i and the recessed portions k are formed to engage each other. A pair of gate trace portions or protrusions m extend from the longitudinally opposite end surfaces of the lens member h. Additional recesses n are formed in the cylinder j to accommodate the gate trace portions m.
In the above-described optical detectors, the cylinder is formed with a sidewall that extends vertically upward to surround the peripheral sidewall of the lens member. However, the recesses formed in the cylinder sidewall do not surround the lens member at the pair of protrusions used for positioning and assembly of the lens member with respect to the cylinder, and the one or more additional protrusions formed by trace amounts of plastic resulting from the molding process. These protrusions extend from the lens member and are received in recesses formed in the sidewall of the cylinder. Since the cylinder must be provided with a sufficient number of recesses to accommodate each of the protrusions, the cylinder has a reduced area in the periphery thereof for which to surround the lens member. Hence, the above-described optical detectors are susceptible to stray light. It is therefore desirable to minimize the number of protrusions extending from the peripheral sidewall of the lens member and the corresponding recesses formed in the cylinder.
Furthermore, during molding, the position of the injection molding port may be varied with respect to the mold cavity of the member. As a result, the die for molding of the cylinder must be changed. This is uneconomical and increases the production cost.
In view of the foregoing shortcomings, it is an object of the present invention to provide an injection molded part having a protrusion formed by an injection molding port located at a non-mating surface of the part.
Another object of the present invention is to provide an optical detector with reduced susceptibility to stray light.
Yet another object of the present invention is to provide an optical detector having a lens member and a cylinder, in which one or more gate trace portions formed on the lens member as a result of injection molding are located at surface of the lens member which does not mate with the cylinder.
Still another object of the present invention is to provide an optical detector having a lens member and a cylinder, wherein one or more gate trace protrusions formed on the lens member as a result of injection molding are formed at positioning protrusions of the lens member used for positioning and/or assembly of the lens member with the cylinder. Where the positioning protrusions at which the gate trace portions are located are plural in number, the positioning protrusions are preferably symmetrically arranged.
To satisfy the above objects and others, the present invention provides an optical detector comprising a lens member for focusing and projecting incident light, a cylinder mounted to the lens member for passing the focused light and blocking extraneous light, and an optical detecting device mounted rearward of the cylinder for receiving the focused light passed through the cylinder. The lens member comprises one or more lenses and a peripheral portion surrounding the lenses, and the lenses and the peripheral portion are preferably integrally molded of a transparent plastic material. Positioning protrusions extend from an outer peripheral surface of the lens member. The cylinder has a sidewall formed with recesses for receiving the positioning protrusions of the lens member. Injection molding port trace portions formed during molding of the lens member protrude from the positioning protrusions and not from a surface of the lens member which mates with a surface of the cylinder.
Since the injection molding port trace portions formed during molding of the lens member are located at the positioning protrusions as described above, a maximum area of the lens member can be surrounded by the cylinder sidewall. Also, if the injection molding port position is modified during molding, it is not necessary to change the die for molding of the cylinder.
In addition, the positioning protrusions in which the gate traces are formed are preferably plural in number and symmetrically arranged.